There has been a constant demand for high-purity water for research and intravenous admixtures. However, it has not yet proved possible to produce water free of everything. Since the water quality requirements vary from one project to another, the tolerable level and the nature of contaminants in the water of course also vary. Therefore, compromises are made with respect to the quality, and the economic requirements in order to obtain water for specific needs. The most common contaminants found in high-purity water are metallic ions, gases, organic compounds, bacteria and their by-products, endotoxins, and mycotoxins.
Ideally, distillation should give water of the highest purity, since the process of purification is merely one of adding heat to convert the water to steam and then condensing the steam to recover the water in pure form. In practice this is not the case because of the difficulties involved in producing water free of all substances.
Many are now convinced that high purity water is not only ideal to have for some research, but is absolutely essential for many biomedical experiments, especially those requiring the injection of parenteral solutions. For this reason, many laboratory distillation devices have been introduced.
Among the known apparatus for producing purified water are those which use multiple distillation techniques as disclosed, for example, in Taylor, "An Apparatus for the Continuous Production of Triple Distilled Water," Journal of Chemical Education, Vol. 37, No. 4, pages 204-205, April 1960. This known apparatus is complex and requires a plurality of distillation flasks and burners.
A system, which includes an overflow regulator and a pressure-controlled shutoff valve, for preparing distilled and deionized water has been proposed in Reasor et al., "Distilled-Deionized Water: A System for Preparing and Distributing Large Volumes," Science, Vol. 161, pages 227-279, July 1968. While relatively large volumes of water can be produced in this known apparatus with little surveillance, secondary storage reservoirs are required.
It has been proposed, in an effort to reduce contamination, to provide systems which both produce and store water free of contact with air. The still and storage reservoir in these known systems are combined so that the distillate is always covered with steam which serves to exclude air. Such a system is disclosed, for example, in Hichman et al., "A Distilling System for Purer Water," Science, Vol. 180, No. 4081, pages 15-24, April 1973. While such systems exclude contaminates which may be carried by ambient air to a considerable extent, contaminates from other sources are not excluded. Other drawbacks also result. The water is maintained at a high temperature, limiting its immediate use. The system is believed to be expensive to operate.
A technique, using chemical action, of purifying water to reduce the level of organic impurities, which cannot be removed by ordinary or oxidative distillation, using pyrocatalytic distillation apparatus has been disclosed in Conway et al., "Ultrapurification of Water for Electrochemical and Surface Chemical Work by Catalytic Pyrodistillation," Analytical Chemistry, Vol. 45, No. 8, pages 1331-1336, July 1973. A considerable amount of energy is required and the probability of inorganic contamination is believed to be high when pyrocatalytic distillation techniques are used.
None of the prior art techniques mentioned above are completely satisfactory for producing high-quality water. Systems in which metals contact water generally produce water containing higher levels of metallic ions than are found in water purified in Pyrex of quartz. It is also generally accepted that waters produced in all-glass distillation apparatus may contain ions leached out from the glass. These include ions of the following elements: Na, K, B, Ca, Pb, As, and Si which are present at parts-per-billion levels. These ions may also be leaching out of laboratory glassware into the water being used in projects. Therefore, this kind of contamination from the still should be of no concern when ordinary glassware is to be used.
A primary source of contamination produced by an all-glass still is the feed water. Metallic and organic contaminants found in distillates usually arise from improper fractionation of the water during the process of distillation. The contaminanted water enters the condenser by entrainment and/or creepage of the liquid along the glass surfaces.
In pharmaceutical work it is important that the water used for the preparation of parenteral solutions be free from endotoxins. The water used for this purpose is normally made by distillation. During distillation, the endotoxins in the feed water carry over by entrainment and contaminante the distillate. In order to prevent endotoxins and other impurities from entering the distilled water, the still must be designed to prevent creepage and entrainment. The water in a storage vessel must also be kept sterile and protected from chemical contamination. The distillation apparatus described here was constructed to produce and store water of the highest possible purity, while requiring minimal operating and maintenance time.
It has also been found that in apparatus for the production of high-purity water which is to operate for long periods, the input water ordinarily should be firstly treated to remove materials which would otherwise cause precipitates, such as carbonates, to collect on the internal surface of the flask.